His vocal credits can be found on the recordings of Aretha Franklin, Luther Vandross, Mick Jagger, Bryan Ferry, Roxy Music, Chic, Diana Ross, Garth Brooks, Ray Charles, Mariah Carey, Steely Dan, David Bowie, Robert Palmer, Patti LaBelle, Al Jarreau, Michael Jackson, Celine Dion, Phoebe Snow, Scritti Politti, Bette Midler, Lady Gaga and many others.

Born in East Harlem, New York, in his early teens, Alfonso {Fonzi} joined neighborhood vocal group, Shades of Jade and befriended a young Luther Vandross.

Thornton and Vandross became soloists with Listen My Brother, the Apollo Theater’s 16 member artist development workshop and sang on camera during the second season of the children's show Sesame Street.

In the late 1970s, approached by producers, Bernard Edwards and Nile Rodgers, Thornton joined the Chic organization as male vocalist on six albums and national concert tours.

After Chic disbanded in the early 1980s, Rodgers and Edwards continued to use the distinct backing vocals of Thornton on chart topping productions for artists like Mick Jagger, Diana Ross, David Bowie, The Power Station and Robert Palmer.

In the spring of 1983, RCA Records released Thornton's debut urban soul-pop album The Leader[4] (co-written and produced) featuring the lead single "Beverly", which reached number 43 on Billboard's R&B chart.